300 ' KANSAS UNIVERSITY SCIENCE BULLETIN. 



dark zone, the denser spot at the center, and, finally, their ap- 

 pearance just at this time. The dark crescent is beyond doubt 

 a collection of food material. Its origin may be, in part, from 

 the nucleus, but mainly, we believe, from the substances 

 brought in by the nurse-cells. Either the chemical composition 

 of this material is such that it is not broken down directly and 

 used, or more food-substance is furnished than the cell can 

 utilize. As new supplies are constantly going in, the pressure 

 becomes greater, and the granular mass grows rnore dense. 

 Finally, close against the nuclear membrane at the widest por- 

 tion of the crescent, and, consequently, at the point of greatest 

 pressure, a spherical mass appears, the vitelline body. I be- 

 lieve the time of appearance of this structure depends upon 

 the supply of food material to the cell. 



The central clear vesicle is perhaps most perplexing. Bal- 

 biani (1) and Munson (6) believe it either to be, or to contain, 

 the centrosome. The former regards it as a functionless centro- 

 some of the female cell, but the latter considers it the centro- 

 some of the dividing oogonia. True, its appearance is different 

 from the surrounding layers of granules, yet it resembles so 

 little a centrosome that appearance will not help us much in 

 discovering its function. The best evidence that it is not the 

 centrosome is its frequent absence, while all other parts of 

 the structure are perfect. In such cases the central space is 

 merely a loose collection of granules, like those of the con- 

 centric layers. This leads me to believe that this central clear 

 vesicle is the result of great pressure of the metaplasm, which 

 might bring about an extraction of certain constituents of the 

 cytoplasm, and these, pushed thus to the center, form the cen- 

 tral sphere of the vitelline body. 



The body next moves from the nuclear membrane, which 

 movement is probably due to increase of metaplasm between 

 the two, or else to a growth of the cytoplasm. 



Yolk now appears in the egg, usually about the periphery, 

 in the form of "yolk-nuclei," described by Foot. In some 

 cases the vitelline body seems to be disintegrating at this stage, 

 breaking up directly into small globules of yolk. This early 

 disappearance is another reason for believing it merely a food 

 body. True, the surrounding metaplasm could disappear at 

 this time and leave the central vesicle to perform its centro- 



